Add new compile-time option NVME_USE_NVD that sets the default value

of the runtime hw.nvme.use_vnd tunable. We still default to nvd unless
otherwise requested.

Sponsored by: Netflix

sys/conf/options

@@ -998,3 +998,6 @@ HN_DEBUG	opt_hn.h
 MMCCAM
 # Encrypted kernel crash dumps
 EKCD		opt_ekcd.h
+
+# NVME options
+NVME_USE_NVD	opt_nvme.h

sys/dev/nvme/nvme_sysctl.c

@@ -27,13 +27,19 @@
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
+#include "opt_nvme.h"
+
 #include <sys/param.h>
 #include <sys/bus.h>
 #include <sys/sysctl.h>
 
 #include "nvme_private.h"
 
-int nvme_use_nvd = 1;
+#ifndef NVME_USE_NVD
+#define NVME_USE_NVD 1
+#endif
+
+int nvme_use_nvd = NVME_USE_NVD;
 
 SYSCTL_NODE(_hw, OID_AUTO, nvme, CTLFLAG_RD, 0, "NVMe sysctl tunables");
 SYSCTL_INT(_hw_nvme, OID_AUTO, use_nvd, CTLFLAG_RDTUN,